Retention and drainage in the manufacture of paper

ABSTRACT

A method of improving retention and drainage in a papermaking process is disclosed. The method provides for the addition of a water soluble copolymer prepared under certain conditions, and a siliceous material to the papermaking slurry. Additionally, a composition comprising a water soluble copolymer, prepared under certain conditions, and a siliceous material and optionally further comprising cellulose fiber is disclosed.

FIELD OF THE INVENTION

This invention relates to the process of making paper and paperboard from a cellulosic stock, employing a novel flocculating system.

BACKGROUND

Retention and drainage is an important aspect of papermaking. It is known that certain materials can provide improved retention and/or drainage properties in the production of paper and paperboard.

The making of cellulosic fiber sheets, particularly paper and paperboard, includes the following: 1) producing an aqueous slurry of cellulosic fiber which may also contain inorganic mineral extenders or pigments; 2) depositing this slurry on a moving papermaking wire or fabric; and 3) forming a sheet from the solid components of the slurry by draining the water.

The foregoing is followed by pressing and drying the sheet to further remove water. Organic and inorganic chemicals are often added to the slurry prior to the sheet-forming step to make the papermaking method less costly, more rapid, and/or to attain specific properties in the final paper product.

The paper industry continuously strives to improve paper quality, increase productivity, and reduce manufacturing costs. Chemicals are often added to the fibrous slurry before it reaches the papermaking wire or fabric to improve drainage/dewatering and solids retention; these chemicals are called retention and/or drainage aids.

As to drainage/dewatering improvement, drainage or dewatering of the fibrous slurry on the papermaking wire or fabric is often the limiting step in achieving faster paper machine speeds. Improved dewatering can also result in a drier sheet in the press and dryer sections, resulting in reduced energy consumption. In addition, as this is the stage in the papermaking method that determines many of the sheet final properties, the retention/drainage aid can impact performance attributes of the final paper sheet.

With respect to solids, papermaking retention aids are used to increase the retention of fine furnish solids in the web during the turbulent method of draining and forming the paper web. Without adequate retention of the fine solids, they are either lost to the mill effluent or accumulate to high levels in the recirculating white water loop, potentially causing deposit buildup. Additionally, insufficient retention increases the papermakers' cost due to loss of additives intended to be adsorbed on the fiber to provide the opacity, strength, sizing or other desirable properties to the paper.

High molecular weight (MW) water-soluble polymers with either cationic or anionic charge have traditionally been used as retention and drainage aids. Recent development of inorganic microparticles, known as retention and drainage aids, in combination with high MW water-soluble polymers, have shown superior retention and drainage efficacy compared to conventional high MW water-soluble polymers. U.S. Pat. Nos. 4,294,885 and 4,388,150 teach the use of starch polymers with colloidal silica. U.S. Pat. Nos. 4,643,801 and 4,750,974 teach the use of a coacervate binder of cationic starch, colloidal silica, and anionic polymer. U.S. Pat. No. 4,753,710 teaches flocculating the pulp furnish with a high MW cationic flocculant, inducing shear to the flocculated furnish, and then introducing bentonite clay to the furnish. U.S. Pat. Nos. 5,274,055 and 5,167,766 disclose using chemically cross-linked organic micropolymers as retention and drainage aids in the papermaking process.

The efficacy of the polymers or copolymers used will vary depending upon the type of monomers from which they are composed, the arrangement of the monomers in the polymer matrix, the molecular weight of the synthesized molecule, and the method of preparation. Moreover, the use of other materials in conjunction with the polymers can provide enhanced retention and/or drainage; there may be other benefits. It is the combination of materials to provide effective retention and/or drainage that is a focus of the present invention.

It had been found recently that water-soluble copolymers when prepared under certain conditions exhibit unique physical characteristics. These polymers are prepared without chemical cross linking agents. Additionally, the copolymers provide unanticipated activity in certain applications including papermaking applications such as retention and drainage aids. There was no prior art suggesting that the unique physical characteristics and unanticipated activity observed would result. The anionic copolymers were disclosed in WO 03/050152 A1, the entire content of which is herein incorporated by reference. The cationic and amphoteric copolymers were disclosed in U.S. Ser. No. 10/728,145, the entire content of which is herein incorporated by reference.

It is known that combinations of materials can provide enhanced overall performance properties. Critical variables include the nature of the materials and the manner in which they are combined. The use of inorganic particles with linear copolymers of acrylamide, is known in the art. Recent patents teach the use of these inorganic particles with water-soluble anionic polymers (U.S. Pat. No. 6,454,902) or specific crosslinked materials (U.S. Pat. No. 6,454,902, U.S. Pat. No. 6,524,439 and U.S. Pat. No. 6,616,806).

However, there still exists a need to improve drainage and retention performance.

It has been found, unexpectedly, that the use of certain inorganic particles in combination with water-soluble copolymers prepared under certain conditions, as disclosed in WO 03/050152 A1, results in enhanced retention and drainage.

SUMMARY OF THE INVENTION

A method of improving retention and drainage in a papermaking process is disclosed. The method provides for the addition of a water soluble copolymer, prepared under certain conditions and a siliceous material to the papermaking slurry.

Additionally, a composition comprising a water soluble copolymer, prepared under certain conditions, and a siliceous material and optionally further comprising cellulose fiber is disclosed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a synergistic combination comprising a water soluble copolymer prepared under certain conditions and siliceous material. It has surprising been found that this synergistic combination results in retention and drainage performance superior to that of the individual components. Synergistic effects occur when the combination of components are used together.

The present invention also provides for a novel composition comprising a water soluble copolymer prepared under certain conditions and a siliceous material.

The present invention also provides for a novel composition comprising a water soluble copolymer prepared under certain conditions and a siliceous material and cellulose fiber.

The use of multi-component systems in the manufacture of paper and paperboard provides the opportunity to enhance performance by utilizing materials that have different effects on the process and/or product. Moreover, the combinations may provide properties unobtainable with the components individually, i.e. synergy occurs.

The water soluble copolymer prepared under certain conditions useful in the present invention can be described as follows:

A water-soluble copolymer composition comprising the formula:

B-co-F

  (I) wherein B is a nonionic polymer segment formed from the polymerization of one or more ethylenically unsaturated nonionic monomers; F is an anionic, cationic or a combination of anionic and cationic polymer segment(s) formed from polymerization of one or more ethylenically unsaturated anionic and/or cationic monomers; the molar % ratio of B:F is from 95:5 to 5:95; and the water-soluble copolymer is prepared via a water-in-oil emulsion polymerization technique that employs at least one emulsification surfactant consisting of at least one diblock or triblock polymeric surfactant wherein the ratio of the at least one diblock or triblock surfactant to monomer is at least about 3:100 and wherein; the water-in-oil emulsion polymerization technique comprises the steps of: (a) preparing an aqueous solution of monomers, (b) adding the aqueous solution to a hydrocarbon liquid containing surfactant or surfactant mixture to form an inverse emulsion, (c) causing the monomer in the emulsion to polymerize by free radical polymerization at a pH range of from about 2 to less than 7.

The anionic copolymer is characterized in that its Huggins' constant (k′) determined between 0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01M NaCl is greater than 0.75; and it has a storage modulus (G′) for a 1.5 wt. % actives of the copolymer solution at 4.6 Hz greater than 175 Pa.

The cationic copolymer is characterized in that its Huggins' constant (k′) determined between 0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01M NaCl is greater than 0.5; and it has a storage modulus (G′) for a 3.0 wt. % actives of the copolymer solution at 6.3 Hz greater than 50 Pa.

The amphoteric copolymer is characterized in that its Huggins' constant (k′) determined between 0.0025 wt. % to 0.025 wt. % of the copolymer in 0.01M NaCl is greater than 0.5; and the copolymer has a storage modulus (G′) for a 1.5 wt. % actives of the copolymer solution at 6.3 Hz greater than 50 Pa.

Inverse emulsion polymerization is a standard chemical process for preparing high molecular weight water-soluble polymers. In general, an inverse emulsion polymerization process is conducted by 1) preparing an aqueous solution of the monomers, 2) adding the aqueous solution to a hydrocarbon liquid containing appropriate emulsification surfactant(s) or surfactant mixture to form an inverse monomer emulsion, 3) subjecting the monomer emulsion to free radical polymerization, and, optionally, 4) adding a breaker surfactant to enhance the inversion of the emulsion when added to water.

Inverse emulsions are typically water-soluble polymers, based upon ionic or non-ionic monomers. Copolymers of two or more monomers can be prepared by the same process. These co-monomers can be anionic, cationic, nonionic, or a combination thereof.

Typical nonionic monomers, include, but are not limited to, acrylamide; methacrylamide; N-alkylacrylamides, such as N-methylacrylamide; N,N-dialkylacrylamides, such as N,N-dimethylacrylamide; methyl acrylate; methyl methacrylate; acrylonitrile; N-vinyl methylacetamide; N-vinyl methyl formamide; vinyl acetate; N-vinyl pyrrolidone; hydroxyalky(meth) acrylates such as hydroxyethyl(meth) acrylate or hydroxypropyl(meth) acrylate; mixtures of any of the foregoing and the like.

Exemplary anionic monomers include, but are not limited to, the free acids and salts of acrylic acid, methacrylic acid; maleic acid; itaconic acid; acrylamidoglycolic acid; 2-acrylamido-2-methyl-1-propanesulfonic acid; 3-allyloxy-2-hydroxy-1-propanesulfonic acid; styrenesulfonic acid; vinylsulfonic acid; vinylphosphonic acid, 2-acrylamido-2-methylpropane phosphonic acid; mixtures of any of the foregoing and the like.

Exemplary cationic monomers include, but are not limited to, cationic ethylenically unsaturated monomers such as the diallyldialkylammonium halides, such as diallyldimethylammonium chloride; the (meth)acrylates of dialkylaminoalkyl compounds, such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethyl aminopropyl (meth)acrylate, 2-hydroxydimethyl aminopropyl (meth)acrylate, aminoethyl (meth)acrylate, and the salts and quaternaries thereof; the N,N-dialkylaminoalkyl(meth)acrylamides, such as N,N-dimethylaminoethylacrylamide, and the salt and quaternaries thereof and mixture of the foregoing and the like.

The co-monomers may be present in any ratio. The resultant copolymer can be non-ionic, cationic, anionic, or amphoteric (contains both cationic and anionic charge). Ionic water soluble polymers, or polyelectrolytes, are typically produced by copolymerizing a non-ionic monomer with an ionic monomer, or by post polymerization treatment of a non-ionic polymer to impart ionic functionality.

The molar percentage of B:F of nonionic monomer to anionic monomer may fall within the range of 95:5 to 5:95, preferably the range is from about 75:25 to about 25:75 and even more preferably the range is from about 65:35 to about 35:65 and most preferably from about 60:40 to about 40:60. In this regard, the molar percentages of B and F must add up to 100%. It is to be understood that more than one kind of nonionic monomer may be present in the Formula I. It is also to be understood that more than one kind of anionic monomer may be present in the Formula I.

In one preferred embodiment of the invention the water-soluble anionic copolymer is defined by Formula I where B, the nonionic polymer segment, is the repeat unit formed after polymerization of acrylamide; and F, the anionic polymer segment, is the repeat unit formed after polymerization of a salt of acrylic acid and the molar % ratio of B:F is from about 75:25 to about 25:75

The physical characteristics of the water-soluble anionic copolymers are unique in that their Huggins' constant (k′) as determined in 0.01M NaCl is greater than 0.75 and the storage modulus (G′) for a 1.5 wt. % actives polymer solution at 4.6 Hz is greater than 175 Pa, preferably greater than 190 and even more preferably greater than 205. The Huggins' constant is greater than 0.75, preferably greater than 0.9 and even more preferably greater than 1.0

The molar percentage of B:F of nonionic monomer to cationic monomer of Formula I may fall within the range of 99:1 to 50:50, or 95:5 to 50:50, or 95:5 to 75:25, or 90:10 to 60:45, preferably the range is from about 85:15 to about 60:40 and even more preferably the range is from about 80:20 to about 50:50. In this regard, the molar percentages of B and F must add up to 100%. It is to be understood that more than one kind of nonionic monomer may be present in the Formula I. It is also to be understood that more than one kind of cationic monomer may be present in the Formula I.

With respect to the molar percentages of the amphoteric copolymers of Formula I, the minimum amount of each of the anionic, cationic and non-ionic monomer is 1% of the total amount of monomer used to form the copolymer. The maximum amount of the non-ionic, anionic or cationic is 98% of the total amount of monomer used to form the polymer. Preferably the minimum amount of any of anionic, cationic and non-ionic monomer is 5%, more preferably the minimum amount of any of anionic, cationic and non-ionic monomer is 7% and even more preferably the minimum amount of any of anionic, cationic and non-ionic monomer is 10% of the total amount of monomer used to form the copolymer. In this regard, the molar percentages of anionic, cationic and non-ionic monomer must add up to 100%. It is to be understood that more than one kind of nonionic monomer may be present in the Formula I, more than one kind of cationic monomer may be present in the Formula I, and that more than one kind of anionic monomer may be present in the Formula I.

The physical characteristics of the water-soluble cationic and amphoteric copolymers are unique in that their Huggins' constant (k′) as determined in 0.01M NaCl is greater than 0.5 and the storage modulus (G′) for a 1.5 wt. % amphoteric or 3.0 wt. % for a cationic actives polymer solution at 6.3 Hz is greater than 50 Pa, preferably greater than 10 and even more preferably greater than 25, or greater than 50, or greater than 100, or greater than 175, or greater than 200. The Huggins' constant is greater than 0.5, preferably greater than 0.6, or greater than 0.75, or greater than 0.9 or greater than 1.0.

The emulsification surfactant or surfactant mixture used in an inverse emulsion polymerization system have an important effect on both the manufacturing process and the resultant product. Surfactants used in emulsion polymerization systems are known to those skilled in the art. These surfactants typically have a range of HLB (Hydrophilic Lipophilic Balance) values that is dependent on the overall composition. One or more emulsification surfactants can be used. The emulsification surfactant(s) of the polymerization products that are used in the present invention include at least one diblock or triblock polymeric surfactant. It is known that these surfactants are highly effective emulsion stabilizers. The choice and amount of the emulsification surfactant(s) are selected in order to yield an inverse monomer emulsion for polymerization.

Diblock and triblock polymeric emulsification surfactants are used to provide unique materials. When the diblock and triblock polymeric emulsification surfactants are used in the necessary quantity unique polymers exhibiting unique characteristic result as described in WO 03/050152 A1. Exemplary diblock and triblock polymeric surfactants include, but are not limited to, diblock and triblock copolymers based on polyester derivatives of fatty acids and poly[ethyleneoxide] (e.g., Hypermer® B246SF, Uniqema, New Castle, Del.), diblock and triblock copolymers based on polyisobutylene succinic anhydride and poly[ethyleneoxide], reaction products of ethylene oxide and propylene oxide with ethylenediamine, mixtures of any of the foregoing and the like. Preferably the diblock and triblock copolymers are based on polyester derivatives of fatty acids and poly[ethyleneoxide]. When a triblock surfactant is used, it is preferable that the triblock contains two hydrophobic regions and one hydrophilic region, i.e., hydrophobe-hydrophile-hydrophobe. Preferably, one or more surfactants are selected in order to obtain a specific HLB value.

The amount (based on weight percent) of diblock or triblock surfactant is dependent on the amount of monomer used. The ratio of diblock or triblock surfactant to monomer is at least about 3 to 100. The amount of diblock or triblock surfactant to monomer can be greater than 3 to 100 and preferably is at least about 4 to 100 and more preferably 5 to 100 and even more preferably about 6 to 100. The diblock or triblock surfactant is the primary surfactant of the emulsification system

A secondary emulsification surfactant can be added to ease handling and processing, to improve emulsion stability, or to alter the emulsion viscosity. Examples of secondary emulsification surfactants include, but are not limited to, sorbitan fatty acid esters, such as sorbitan monooleate (e.g., Atlas G-946, Uniqema, New Castle, Del.), ethoxylated sorbitan fatty acid esters, polyethoxylated sorbitan fatty acid esters, the ethylene oxide and/or propylene oxide adducts of alkylphenols, the ethylene oxide and/or propylene oxide adducts of long chain alcohols or fatty acids, mixed ethylene oxide/propylene oxide block copolymers, alkanolamides, sulfosuccinates and mixtures thereof and the like.

Polymerization of the inverse emulsion may be carried out in any manner known to those skilled in the art, for example see Allcock and Lampe, Contemporary Polymer Chemistry, (Englewood Clifs, N.J., PRENTICE-HALL, 1981), chapters 3-5.

A representative inverse emulsion polymerization is prepared as follows. To a suitable reaction flask equipped with an overhead mechanical stirrer, thermometer, nitrogen sparge tube, and condenser is charged an oil phase of paraffin oil (135.0 g, Exxsol® D80 oil, Exxon—Houston, Tex.) and surfactants (4.5 g Atlas®G-946 and 9.0 g Hypermer® B246SF). The temperature of the oil phase was then adjusted to 37° C.

An aqueous phase is prepared separately which comprised 53-wt. % acrylamide solution in water (126.5 g), acrylic acid (68.7 g), deionized water (70.0 g), and Versenex® 80 (Dow Chemical) chelant solution (0.7 g). The aqueous phase is then adjusted to pH 5.4 with the addition of ammonium hydroxide solution in water (33.1 g, 29.4 wt. % as NH₃). The temperature of the aqueous phase after neutralization is 39° C.

The aqueous phase is then charged to the oil phase while simultaneously mixing with a homogenizer to obtain a stable water-in-oil emulsion. This emulsion is then mixed with a 4-blade glass stirrer while being sparged with nitrogen for 60 minutes. During the nitrogen sparge the temperature of the emulsion is adjusted to 50±1° C. Afterwards, the sparge was discontinued and a nitrogen blanket implemented.

The polymerization is initiated by feeding a 3-wt. % solution of 2,2′-azobisisobutyronitrile (AIBN) in toluene (0.213 g) over a period of 2 hours. This corresponds to an initial AIBN charge, as AIBN, of 250 ppm on a total monomer basis. During the course of the feed the batch temperature was allowed to exotherm to 62° C. (˜50 minutes), after which the batch was maintained at 62±1° C. After the feed the batch was held at 62±1° C. for 1 hour. Afterwards 3-wt. % AIBN solution in toluene (0.085 g) is then charged in under one minute. This corresponds to a second AIBN charge as AIBN of 100 ppm on a total monomer basis. Then the batch is held at 62±1° C. for 2 hours. Then batch is then cooled to room temperature, and breaker surfactant(s) is added.

The inventive copolymer is typically diluted at the application site to produce an aqueous solution of 0.1 to 1% active copolymer. This dilute solution of the inventive copolymer is then added to the paper process to affect retention and drainage. The inventive copolymer may be added to the thick stock or thin stock, preferably the thin stock. The copolymer may be added at one feed point, or may be split fed such that the copolymer is fed simultaneously to two or more separate feed points. Typical stock addition points include feed point(s) before the fan pump, after the fan pump and before the pressure screen, or after the pressure screen.

The copolymer may be added in any effective amount to achieve flocculation. Preferably, the copolymer is employed in an amount of at least about 0.07 lb. to about 1 lbs. of active copolymer per ton of cellulosic pulp, based on the dry weight of the pulp. The amount of copolymer could be more than 1 lb/ton. The concentration of copolymer is preferably from about 0.1 to about 1 lbs. of active copolymer per ton of dried cellulosic pulp. More preferably the copolymer is added in an amount of from about 0.1 to 0.75 of from about 0.2 to about 0.6 lb per ton based on dry weight of the cellulosic pulp.

Siliceous materials can be used as a component of a retention and drainage aid used in making paper and paperboard. The siliceous material may be any of the materials selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, polysilicic acid, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites and swelling or swellable clays. These materials are characterized by the high surface charge, high charge density and submicron particle size.

This group includes stable colloidal dispersion of spherical amorphous silica particles, referred to in the art as silica sols. The term sol refers to a stable colloidal dispersion of spherical amorphous particles. Silica gels are three dimensional silica aggregate chains, each comprising several amorphous silica sol particles, that can also be used in retention and drainage aid systems; the chains may be linear or branched. Silica sols and gels are prepared by polymerizing monomeric silicic acid into a cyclic structure that result in discrete amorphous silica sols of polysilicic acid. These silica sols can be reacted further to produce three-dimensional gel network. The various silica particles (sols, gels, etc.) can have an overall size of 5-50 nm. Anionic colloidal silica can also be used.

Clay is another type of inorganic particle. The term clay is applied to a number of mineral groups considered to be phyllosilicates, a subclass of silicates. Clays, therefore, include chlorites, illites, kaolinites and smectites. Smectites are swellable clays, examples include, but are not limited to hectorite, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites and sepiolites, and the like. The chemical and physical nature of these materials is described in Aloi, F. G., and Trsksak, R. M., in Retention and Fines Fillers During Papermaking, J. M. Gess, ed., TAPPI Press, 1998, Chapter 5, p. 61-108.

Montmorillonite is a common swellable clay used in the art. Montmorillonite has a di-octahedral structure and a strong negative charge in water. It is the high anionic charge, electrical double layer in solution, and small particle size that make montmorillonite a colloidal particle. Bentonite, the most common clay now in commercial use in retention drainage, is predominately montmorillonite.

Bentonite is a term in the art applied to a class of clay materials, typically aggregates of two or more minerals. These mineral aggregates occur naturally, although these materials may undergo chemical and/or physical processing to modify their properties. The major component, due to its interactions with water, is montmorillonite. Montmorillonites are three-dimensional particles up to 2000 nm long with a thin uniform thickness of <1 nm and consist of oxygen, silicon, and a metal ion, typically aluminum and/or magnesium.

Other inorganic particles can be used, including, but not limited to, aluminum hydroxide, perlite, zeolite and vermiculite.

The siliceous material can be added to the cellulosic suspension in an amount of at least 0.01 lb per ton based on dry weight of the cellulosic suspension. The amount of siliceous material may be as high as 100 lb per ton. Preferably, the amount of siliceous material is from about 0.1 lb/ton to about 50 lb/ton. Even more preferably the amount of siliceous material is from about 0.5 to about 10 lb/ton based on the dry weight of the cellullosic suspension.

The siliceous material and water soluble copolymer components may be added substantially simultaneously to the cellulosic suspension. For instance, the two components may be added to the cellulosic suspension separately but at the same stage or dosing point. When the components of the inventive system are added simultaneously the siliceous material and the water soluble copolymer may be added as a blend. The mixture may be formed in-situ by combining the siliceous material and the water soluble copolymer at the dosing point or in the feed line to the dosing point. Alternatively the inventive system comprises a preformed blend of the siliceous material and water soluble copolymer.

In an alternative form of the invention the components of the inventive system are added sequentially. A shear point may or may not be present between the addition points of the components. The components can be added in either order.

The inventive system is typically added to the paper process to affect retention and drainage. The inventive system may be added to the thick stock or thin stock, preferably the thin stock. The system may be added at one feed point, or may be split fed such that the inventive system is fed simultaneously to two or more separate feed points. Typical stock addition points included feed points(s) before the fan pump, after the fan pump and before the pressure screen, or after the pressure screen.

The amount of siliceous material in relationship to the amount of copolymer used in the present invention can be about 100:1 to about 1:100 by weight, or from about 50:1 to 1:50 or about 10:1 to 1:10.

Optionally, an additional component of the retention and drainage aid system can be a conventional flocculant. The additional component of the retention and drainage system is added in conjunction with the siliceous material and the water soluble copolymer made under certain conditions to provide a multi-component system which improves retention and drainage.

The components may be added substantially simultaneously to the cellulosic suspension. For instance, the components may be added to the cellulosic suspension separately but at the same stage or dosing point. When the components of the inventive system are added simultaneously they may be added as a blend. The mixture may be formed in-situ by combining the components at the dosing point or in the feed lines(s) to the dosing point. Alternatively, the inventive system comprises a preformed blend of the various components. In another alternative form of the invention the components of the inventive system are added sequentially. A shear point may or may not be present between the addition points of the components. The components can be added in any order.

The inventive system is typically added to the paper process to affect retention and drainage. The inventive system may be added to the thick stock or thin stock, preferably the thin stock. The system may be added at one feed point, or may be split fed such that the inventive system is fed simultaneously to two or more separate feed points. Typical stock addition points included feed points before the fan pump, after the fan pump and before the pressure screen, or after the pressure screen.

The conventional flocculant can be an anionic, cationic or non-ionic polymer. The ionic monomers are most often used to make copolymers with a non-ionic monomer such as acrylamide. These polymers can be provided by a variety of synthetic processes including, but not limited to, suspension, dispersion and inverse emulsion polymerization. For the last process, a microemulsion may also be used.

The co-monomers of the conventional flocculant may be present in any ratio. The resultant copolymer can be non-ionic, cationic, anionic, or amphoteric (contains both cationic and anionic charge). Ionic water-soluble polymers, or polyelectrolytes, are typically produced by copolymerizing a non-ionic monomer with an ionic monomer, or by post polymerization treatment of a non-ionic polymer to impart ionic functionality.

Yet other additional components that can be part of the inventive system are aluminum sources such as alum (aluminum sulfate), polyaluminum sulfate, polyaluminum chloride and aluminum chlorohydrate.

EXAMPLES

To evaluate the performance of the present invention, a series of drainage tests were conducted utilizing a synthetic alkaline furnish. This furnish is prepared from hardwood and softwood dried market lap pulps, and from water and further materials. First, the hardwood and softwood dried market lap pulp are refined separately. These pulps are then added at a specific ratio to an aqueous medium. The aqueous medium utilized in preparing the furnish comprises a mixture of local hard water and deionized water to a representative hardness. Inorganic salts are added in amounts so as to provide this medium with a representative alkalinity and conductivity. Precipitated calcium carbonate (PCC) is introduced into the pulp furnish at a representative weight percent. The drainage tests were conducted by mixing the furnish with a mechanical mixer at a specified mixer speed, and introducing the various chemical components into the furnish and allowing the individual components to mix for a specified time prior to the addition of the next component. The specific chemical components and dosage levels are described in the data tables. The drainage activity of the invention was determined utilizing either the Canadian Standard Freeness (CSF) or a Vacuum Drainage Test (VDT). The CSF test, a commercially available device (Lorentzen & Wettre, Stockholm, Sweden) can be utilized to determine relative drainage rate or dewatering rate is also known in the art; standard test method (TAPPI Test Procedure T-227) is typical. The CSF device consists of a drainage chamber and a rate measuring funnel, both mounted on a suitable support. The drainage chamber is cylindrical, fitted with a perforated screen plat and a hinged plate on the bottom, and with a vacuum tight hinged lid on the top. The rate-measuring funnel is equipped with a bottom orifice and a side, overflow orifice.

The CSF drainage tests are conducted with 1 liter of the furnish. The furnish is prepared for the described treatment externally from the CSF device in a square beaker to provide turbulent mixing. Upon completion of the addition of the additives and the mixing sequence, the treated furnish is poured into the drainage chamber, closing the top lid, and them immediately opening the bottom plate. The water is allowed to drain freely into the rate-measuring funnel; water flow that exceeds that determined by the bottom orifice will overflow through the side orifice and is collected in a graduated cylinder. The values generated are described in milliliters (ml) of filtrate; higher quantitative values represent higher levels of drainage or dewatering.

Drainage tests may also be conducted utilizing a vacuum drainage test (VDT). The results of this testing demonstrate the ability of the VDT to differentiate drainage aids by the magnitude of the drainage time. The device setup is similar to the Buchner funnel test as described in various filtration reference books, for example see Perry's Chemical Engineers' Handbook, 7^(th) edition, (McGraw-Hill, New York, 1999) pp. 18-78. The VDT consists of a 300-ml magnetic Gelman filter funnel, a 250-ml graduated cylinder, a quick disconnect, a water trap, and a vacuum pump with a vacuum gauge and regulator. The VDT test is conducted by first setting the vacuum to the desired level, typically 10 inches Hg, and placing the funnel properly on the cylinder. Next, 250 g of 0.5% wt. % paper stock is charged into a beaker and then the required additives according to treatment program (e.g., starch, alum, and testing flocculants) are added to the stock under the agitation provided by an overhead mixer. The stock is then poured into the filer funnel and the vacuum pump is turned on while simultaneously starting a stopwatch. The drainage efficacy is reported as the time, in seconds, required to obtain 230 ml of filtrate. Lower quantitative drainage time values represent higher levels of drainage or dewatering, which is the desired response.

The tables (below) illustrate the utility of the invention. The test samples were prepared as follows: to the furnish prepared as described above is added, first, 10 lbs. of cationic starch (Stalok®400, A.E. Staley, Decatur, Ill.) per ton of furnish (dry basis) and then 5 lbs. of alum (aluminum sulfate-octa hydrate obtained from Delta Chemical Corporation, Baltimore, Md. as a 50% solution) per ton of furnish (dry basis). The additive(s) of interest, as noted in the tables, were then added.

The following materials are used in the examples provided in the tables. SP9232 is PerForm® SP9232, a retention and drainage aid produced under certain conditions (see WO 03/050152 A1); PC8138 is PerForm® PC8138 a cationic copolymer of polyacrylamide; PA8137 is PerForm® PA8137, an anionic copolymer of acrylamide; and PM9025 is PerForm® PM9025, a colloidal silica sol. PerForm is a trademark of Hercules Incorporated, Wilmington, Del. Bentolite® HS is a water swellable bentonite clay (Southern Clay, Gonzales, Tex.). Polyflex® CP.3 is a polymeric microbead (Ciba, Tarrytown, N.Y.).

Table 1 provides the CSF drainage of an embrodiment of the invention. TABLE 1 Example #/T #/T CSF # Additive #1 (active) Additive #2 (active) ml Comments 1 None 410 2 SP 9232 0.4 520 3 SP9232/PM9025 0.4/2 625 Premixed 4 PC 8138 0.4 None 435 5 PC 8138 0.4 SP 9232 0.4 595 6 PC 8138 0.4 SP9232/PM9025 0.4/2 695 Premixed 7 PA 8137 0.2 None 495 8 PA 8137 0.2 SP9232 0.4 595 9 PA 8137 0.2 SP9232/PM9025 0.4/2 650 Premixed 10 SP 9232 0.2 None 450 11 SP 9232 0.2 PM 9025 2 590 12 PM9025 2 585

Another embodiment of the present invention is illustrated in Table 2, where a series of vacuum drainage test (VDT) were conducted TABLE 2 Example # Additive #/T (active) VDT, s 13 None 0   49.2 14 SP 9232 0.3 32.5 15 SP 9232 0.6 24.3 16 Bentolite HS 3   32.8 17 Bentolite HS 6   29.2 18 SP 9232/Bentolite HS 0.3/3 26.3 19 SP 9232/Bentolite HS 0.6/3 21.0 20 SP 9232/Bentolite HS 0.3/6 24.1 21 SP 9232/Bentolite HS 0.6/6 20.1

The data in Tables 1 and 2 illustrate the improved drainage of the present invention, when a silica sol or water swellable clay is added to the paper furnish in combination with the SP9232.

Yet another example of the inventive process is provided in Table 3, where a series of CSF drainage tests were conducted. TABLE 3 PA Example 8137 Drainage Aid #/T Drainage Aid # #/T #1 (active) #2 #/T CSF 22 0.2 495 23 0.4 550 24 0.2 SP 9232 0.2 565 25 0.4 0.4 660 26 0.2 Polyflex CP. 3 0.2 590 27 0.4 0.4 655 28 0.2 SP 9232 0.2 PM 9025 1 640 29 0.4 0.4 2 700 30 0.2 SP 9232 0.2 Bentolite HS 2 600 31 0.4 0.4 4 690 32 0.2 Polyflex CP. 3 0.2 PM 9025 1 645 33 0.4 0.4 2 690 34 0.2 Polyflex CP. 3 0.2 Bentolite HS 2 575 35 0.4 0.4 4 670

The data in Table 3 illustrate the improved drainage activity of the inventive process when a conventional flocculant, an anionic polyacrylamide PA 8137, is added to the combination of the polymeric microbead or the water-soluble anionic polymer produced under certain conditions, and the siliceous material.

EXAMPLE 36

Laboratory retention studies were conducted utilizing a furnish from a paper machine which produced a 43 lb/3000 ft² wood free sheet containing 20% calcium carbonate filler. First pass retention data were determined using a Britt Jar according to TAPPI test method T-261. A cationic polyacrylamide (Percol®182, a product of Ciba Specialty Chemicals, Tarrytown, N.Y.) was added at a level of 0.32 lb/ton to the examples listed in Table 4. TABLE 4 Example # Additive FPR (%) 36A Control (No drainage aid component) 76.3 36B Silica (8 lb/ton) 85.2 36C SP9232 (1.3 lb/ton) 84.7 36D SP9232 and Silica (0.25 lb/ton and 4.6 lb/ton 86.8

All dose rates are on an as product received basis.

Silica is NP822 structured silica, a product of Eka Chemicals, Marietta, Ga. SP9232 is PerForm™ SP9232 retention and drainage aid, a product of Hercules Incorporated, Wilmington, Del.

This example indicates that the combination of the two additives provides an improvement over the individual components, even when the level of the components is lower than that used individually.

EXAMPLE 37

Laboratory retention and drainage studies were conducted utilizing a furnish from a paper machine which produced a 50 lb/3000 ft² wood free sheet containing 20% calcium carbonate filler. First pass retention data were determined using a Britt Jar (TAPPI test method R-261) and drainage were determined, using Britt Jar in combination with the Canadian Standard Freeness test (TAPPI test method T-261). A cationic polyacrylamide (Percol 47, a product of Ciba Specialty Chemicals, Tarrytown, N.Y.) was added at a level of 0.7 lb/ton to the examples listed in Table 5. TABLE 5 Example Additive Drainage (mls) FP Fines Retn (%) 37A Control (8 lb/ton 480 64.5 Bentonite) 37B SP9232 (0.4 lb/ton 485 65.1 and Bentonite (5 lb/ton 37C SP9232 (0.4 lb/ton) 510 69.8 and Silica (2 lb/ton) 37D SP9232 (0.4 lb/ton) 525 72.7 and Silica (4 lb/ton)

All dose rates are on an as product received basis.

Silica is PerForm™ PM9025 microparticle retention and drainage aid and SP9232 is PerForm™ SP9232 retention and drainage aid; both are products of Hercules Incorporated, Wilmington, Del. Bentonite is Hydrocol, a swellable clay product of Ciba Specialty Chemicals, Tarrytown, N.Y.

The data in Table 5 indicate that SP9232 improves the retention and drainage when used in combination with bentonite, even at lower levels of bentonite (Example 37B). Furthermore, these values are improved when silica is used. 

1. A method of improving retention and drainage in a papermaking process wherein the improvement comprising adding to the papermaking slurry a water soluble copolymer and a siliceous material, wherein the water soluble copolymer comprising the formula:

B-co-F

  (I) wherein B is a nonionic polymer segment formed from the polymerization of one or more ethylenically unsaturated nonionic monomers; F is an anionic, cationic or a combination of anionic and cationic polymer segment(s) formed from polymerization of one or more ethylenically unsaturated anionic or cationic monomers; and the water-soluble copolymer is prepared via a water-in-oil emulsion polymerization technique that employs at least one emulsification surfactant comprising at least one diblock or triblock polymeric surfactant wherein the amount of the at least one diblock or triblock surfactant to monomer is at least about 3:100 and wherein the water-in-oil emulsion polymerization technique comprises the steps: (a) preparing an aqueous solution of monomers, (b) adding the aqueous solution to a hydrocarbon liquid containing surfactant or surfactant mixture to form an inverse emulsion, (c) causing the monomer in the emulsion to polymerize by free radical polymerization at a pH range of from about 2 to less than
 7. 2. The method of claim 1 wherein the siliceous material is selected from the group consisting of silica based particles, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites and combinations thereof.
 3. The method of claim 1 wherein the siliceous material is a swellable clay.
 4. The method of claim 3 wherein the swellable clay is a bentonite type clay.
 5. The method of claim 3 wherein the swellable clay is a smectite.
 6. The method of claim 3 wherein the swellable clay is selected from the group consisting of hectorite, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites and sepiolites and combinations thereof.
 7. The method of claim 1 wherein the siliceous material and water soluble copolymer are added to the cellulosic suspension as a blend or simultaneously.
 8. The method of claim 1 wherein the siliceous material is added to the cellulosic suspension prior to the addition of the water soluble copolymer.
 9. The method of claim 1 wherein the water soluble copolymer is anionic.
 10. The method of claim 1 wherein non-ionic monomer comprises acrylamide and the anionic monomer comprises a salt of acrylic acid.
 11. The method of claim 1 wherein the water soluble copolymer is cationic.
 12. The method of claim 1 wherein the water soluble copolymer comprises both anionic and cationic monomers.
 13. The method of claim 1 wherein the system comprises an additional component wherein the additional component comprises a conventional flocculant.
 14. The method of claim 1 wherein the system comprises an additional component wherein the additional component comprises an aluminum source.
 15. The method of claim 1 wherein the amount of water soluble copolymer is from about 0.01 lb/ton to about lb/ton based on the dry weight of pulp.
 16. The method of claim 1 wherein the amount of siliceous material is from about 0.01 to about 100 lb/ton based on the dry weight of pulp.
 17. A composition comprising a water soluble copolymer and a siliceous material wherein the water soluble copolymer comprising the formula:

B-co-F

  (I) wherein B is a nonionic polymer segment formed from the polymerization of one or more ethylenically unsaturated nonionic monomers; F is an anionic, cationic or a combination of anionic and cationic polymer segment(s) formed from polymerization of one or more ethylenically unsaturated anionic or cationic monomers; and the water-soluble copolymer is prepared via a water-in-oil emulsion polymerization technique that employs at least one emulsification surfactant comprising at least one diblock or triblock polymeric surfactant wherein the amount of the at least one diblock or triblock surfactant to monomer is at least about 3:100 and wherein the water-in-oil emulsion polymerization technique comprises the steps: (a) preparing an aqueous solution of monomers, (b) adding the aqueous solution to a hydrocarbon liquid containing surfactant or surfactant mixture to form an inverse emulsion, (c) causing the monomer in the emulsion to polymerize by free radical polymerization at a pH range of from about 2 to less than
 7. 18. The composition of claim 17 further comprising cellulosic fiber.
 19. The composition of claim 17 wherein the water soluble copolymer is anionic.
 20. The composition of claim 17 wherein the water soluble copolymer is cationic or amphoteric. 